Radio Mic Frequencies

[Pete Alcock]

Hi All,

 

I have been researching radio mic frequencies after building myself a (rather handsome) racked-up kit of four JTS receivers and associated handhelds.

 

It all works splendidly apart from intermodulation between the transmitters, and they're also affecting my adjacent Shures when I try to use the whole lot together. I've experimented with different frequencies, however have come up with the following problems:

 

1. Within the UHF shared frequencies there are only two that I can set the JTS systems to! I can get close (I can set 854.875 but not the proper 854.900 for example). This appears to be a shortcoming of the otherwise excellent JTS UHF series. Anyone else found this? Is it potentially illegal even?

 

2. To avoid intermodulation, do you just have to try various combinations until you find one where everything works (very tedious and will take ages), or is there a rule of thumb to do with how the frequencies are related mathmatically? Failing that what does everybody else do?

 

How close in frequencies do multi-mic systems operate on, in "big" situations like the west end?

 

Any advice will be appreciated as always.

 

Cheers,

 

Pete.

[Just Some Bloke]

This page from Trantec should solve your problems.

[Pete McCrea]

we've just put out a 12 channel radio mic system for a UK with 'Dancing in the Street', with about xxx.500 between the different RX units. We are licensed to go into licensed frequencies.

[david.elsbury]

Those JTS are really REALLY tricky to get a good set of frequenices for.

I spent about 2 days on it, trying to get two racks to work together...

I referred to the Audio-Technica website, their intermod calculator.

When I get into work later today, I'll post back on the frequencies of our 8.

Nice mics, for the money, though. Which JTS are they? And are you using antenna distribution?

 

David

[Bobbsy]

The Audio Technica site has a very useful page for this at:

 

http://ff.audiotechnica.com/using/wireless/compat/index.html

 

You can plug in your selection of frequencies and it warns what intermod problems to expect.

 

Bob

[david.elsbury]

JTS Frequencies

• 782.625
  
• 783.000
  
• 785.875
  
• 788.625
  
• 768.000
  
• 792.750
  
• 794.125
  
• 794.875
  

The Audio Technica site has a very useful page for this at:

 

http://ff.audiotechnica.com/using/wireless/compat/index.html

 

You can plug in your selection of frequencies and it warns what intermod problems to expect.

 

Bob

Yep, that's the one I used.

[Bobbsy]

Just a couple of notes on that frequency list...

 

First, here in the UK, to use those frequencies you, by law, should have a licence which can be obtained by contacting JFMG at http://www.jfmg.co.uk/ . Such a licence will be site-specific because...

 

(seguing neatly to point two)

 

Depending where you are in the UK, those frequenices could be subject to TV interference...or to you interferring with TV. That part of the spectrum is pretty crowded since the advent of Channel 5 and Digital TV.

 

Bob

[Pete Alcock]

Thank you to the responders above, especially David from NZ and Bobsy, for the very useful info. The AudioTechnica online frequency calculator is fascinating and I've managed to find a set of frequencies that should be OK from a standpoint of intermod avoidance, however, they're not within the UK "Shared Frequencies" band.

 

In response to your queries David, I'm using the JTS MH950 and PT950 together with four US901 receivers and the antenna distro. The fequencies you list as being OK, are way outside the UK band - unforunately, I don't think the UK version even supports them.

 

I'll get in touch with the UK JTS distributor tomorrow and see what they say - It's all very well the gear having 193 frequencies, but if only 2 or 3 are actually licensable in the UK, it makes thinking of hiring them out a somewhat futile exercise!

 

I'll advise in due course.

 

Pete.

[Bobbsy]

Hi Pete, and thanks for the kind words.

 

I don't know the JTS gear myself (tend to use Sennheiser, Sony and, at a pinch, Audio Ltd and Micron gear).

 

However, before despairing of getting a licence for the frequencies you CAN do it's likely worth giving JFMG a call. Their number is on that link I posted. In my experience, they will do their best to help you and/or make suggestions.

 

Bob

[Pete Alcock]

To conclude this topic, I have spoken to JFMG and JTS' distributor Proel, both who were very helpful. The JTS kit is limited to 125kHz increments in frequency setting, so unfortunately you can only set 2 of the UK shared frequencies (857.625 and 861.750), although you can set the following within the "No license required" area of the band:

 

865.000

863.250

864.625

863.750

 

I've checked these 4 for intermodulation and they seem OK.

 

The other alternative is to apply to JFMG for specific frequencies outside the shared frequencies which could be specially licensed if they're available in your area.

 

Trust this is useful for anyone else with the otherwise excellent JTS mics.

 

Pete.

[Chappie]

This page from Trantec should solve your problems.

<{POST_SNAPBACK}>

I know you have probably solved your issues by now, but I just want to point out something to anyone who is interested. The tables that manufacturers use to allow you to cram their systems closer together may not nessecerrily work with other makes. The Trantec tables, for example, will cause you lots of problems if you try them with Shure systems due to differences in modulation, squelch keys and general design differences. Some makes need far more distance apart than others.